DESCRIPTION (adapted from the application) Disturbances of potassium homeostasis can result in fatal consequences such as cardiac arrest. The kidney is a vital organ that maintains serum potassium concentration in a very narrow range. To achieve this, renal epithelial cells are equipped with membrane transporters such as Na-ATPase and K channels. The exact mechanism of K absorption and secretion in the kidney is not completely understood, however, recent progress suggests that potassium channels may play an important role in the process. In addition to inward rectifier K channels, voltage-gated K channels are also expressed in kidney. Dr. Gary Desir's laboratory has identified several such channels. Two of these have been extensively characterized: Kv1.3 and KCNA10. Although the precise physiological role of these channels in renal K homeostasis is unclear, it is postulated that Kv1.3, in conjunction with ATP-sensitive KATP channels, mediates K exit into interstitium where K can be returned to blood stream or accumulated and recycled back into the cell by Na+,K+-ATPase pump. KCNA10 may participate in K transport, the regulation of vascular tone, the cardiac action potential, and cortisol secretion. To test these hypotheses, I will examine the sub-cellular localization of Kv1.3 in the renal epithelia, and study the Kv1.3 function in vivo using gene-targeting. The Specific Aims of the project are: (1) Localization of Kv1.3 in renal epithelial cells. (2) Generation of Kv1.3-deficient mice. (3) Characterization of the K0.3-deficient mice. (4) Generation of KCNA10 knockout mouse and Kv1.3/KCNA10 double knockout mouse.